The Grim Reaper (or just Grim) is the overall titular main protagonist of the franchise. He is an undead skeleton personification of Death, who speaks with a Jamaican accent. After having lost to Billy and Mandy after Mandy cheated in a limbo contest over the soul of Mr. Snuggles (and also the soul of Billy himself), Grim is now forced to be their best friend forever. If Grim does not live up to his commitment, he will be stripped of his powers and be forced to spend eternity in Underworld Jail.

Grim is often stuck with cleaning-up the consequences of mishaps that are in no small part due to Billy's stupidity and lack of common sense. On Mandy's part, Grim is often forced to do her chores and obey her direct orders, as her unwilling slave. It is stated several times in the series that he does the dishes every single day for Billy and Mandy ever since they first met which he seriously despises.

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